Arbuscular Mycorrhizal Fungi Alter Fractal Dimension Characteristics of Robinia pseudoacacia L. Seedlings Through Regulating Plant Growth,Leaf Water Status,Photosynthesis, and Nutrient Concentration Under Drought Stress

The influence of arbuscular mycorrhizal fungi (AMF), Funneliformis mosseae and Rhizophagus intraradices, on plant growth, leaf water status, chlorophyll concentration, photosynthesis, nutrient concentration, and fractal dimension (FD) characteristics of black locust (Robinia pseudoacacia L.) seedlings was studied in pot culture under well-watered, moderate drought stress, and severe drought stress treatments. Mycorrhizal seedlings had higher dry biomass, leaf relative water content (RWC), and water use efficiency (WUE) compared with non-mycorrhizal seedlings. Under all treatments, AMF colonization notably enhanced net photosynthetic rate, stomatal conductance, and transpiration rate, but decreased intercellular CO₂ concentration. Leaf chlorophyll a and total chlorophyll concentrations were higher in AM seedlings than those in non-AM seedlings although there was no significant difference between AMF species. AMF colonization improved leaf C, N, and P concentrations, but decreased C:N, C:P, and N:P ratios. Mycorrhizal seedlings had a larger FD value than non-mycorrhizal seedlings. The FD value was positively and significantly correlated to the plant growth parameters, photosynthesis, RWC, WUE, and nutrient concentration but negatively correlated to leaf/stem ratio, C:N and C:P ratios, and intercellular CO₂ concentration. We conclude that AMF lead to an improvement of growth performance of black locust seedlings under all growth conditions, including drought stress via improving leaf water status, chlorophyll concentration, photosynthesis, and nutrient uptake. Moreover, FD technology proved to be a powerful non-destructive method to characterize the effect of AMF on the physiology of host plants during drought stress.     

Is genotypic variation of H⁺ efflux under P deficiency linked with nodulated-root respiration of N₂ fixing common-bean (Phaseolus vulgaris L.)?

To examine genotypic variation of common bean in growth, phosphorus uptake, nodulated-root proton release, and nodule gas permeability, seven common bean recombinant inbred lines (RIL) from the cross of BAT477×DOR364 were inoculated by Rhizobium tropici CIAT 899 and grown in hydroaeroponic culture under glasshouse conditions. A positive correlation was observed between shoot and nodule biomass for most of the studied RILs. Under P deficiency, the tolerant common bean RILs acidified more of their rhizosphere than the sensitive ones. The proton release of the RILs 147, 124, 104, 75 and RIL34 was positively correlated with nodule O? permeability. We conclude that nodulated common bean plants release a substantial amount of H? into the rhizosphere that is linked to the symbiotic N? fixation. It depends upon the nodule permeability to O? diffusion, and varies with genotype.     

Growth, nitrogen fixation and ammonium assimilation in common bean (Phaseolus vulgaris): effect of phosphorus

The impact of phosphorous nutrition on plant growth, symbiotic N₂ fixation, ammonium assimilation, carbohydrate and amino-acid accumulation, as well as on nitrogen, phosphorus and ATP content in tissues in common bean ( Phaseolus vulgaris ) plants was investigated. Plants inoculated with Rhizobium tropici CIAT899 were grown in Leonard jars under controlled conditions, with P-deficient (0 and 0.1 m M ), P-medium (0.5, 1 and 1.5 m M ) and P-high (2 m M ) conditions in a N-free nutrient solution. The P application, increased leaf area, whole plant DW (67%), nodule biomass (4-fold), and shoot and root P content (4- and 6-fold, respectively) in plant harvested at the onset of flowering (28-days-old). However, P treatments decreased the total soluble sugar and amino acid content in vegetative organs (leaf, root and nodules). The root growth proved less sensitive to P deficiency than did shoot growth, and the leaf area was significantly reduced at low P-application. The absence of a relationship between shoot N content, and P levels in the growth medium could indicate that nitrogen fixation requires more P than does plant growth. The optimal amount for the P. vulgaris – R. tropici CIAT899 symbiosis was 1.5 m M P, this treatment augmented nodule-ARA 20-fold, and ARA per plant 70-fold compared with plants without P application.     

Arbuscular mycorrhizal fungi enhance P uptake and alter plant morphology in the invasive plant Microstegium vimineum

Invasive plant species can interact with native soil microbes in ways that change how they use nutrients and allocate biomass. To examine whether Microstegium vimineum form symbiotic associations with arbuscular mycorrhizal fungi (AMF) and whether AMF mediate nutrient acquisition and growth of the plant, we conducted a field survey in Raleigh, NC and Hangzhou, China and two experiments in growth chambers. This is the first report that M. vimineum is mycorrhizal, with colonization rates of 47 and 21 % in its native and invaded range, respectively. In the growth chamber, addition of an AMF inoculum mixture significantly promoted M. vimineum biomass accumulation in both field and sterilized soils, particularly after 64 days of growth. Arbuscular mycorrhizal fungi also increased plant phosphorous (P) uptake but did not consistently affect total plant nitrogen (N) acquisition, leading to decreases in plant N:P ratios. More interestingly, AMF significantly altered plant morphology, increasing the number of stolons and aerial roots per individual (59 and 723 %), aerial roots per gram aboveground biomass (374 %) and aerial roots per stolon (404 %). Our results suggest that mycorrhizal enhancement of plant growth by stimulating tillering may serve as another mechanism by which M. vimineum can quickly take over new territory. Future studies on invasive plant-microbial interactions are needed to understand the mechanisms through which microbes contribute to the competitive ability of invasive plants.     

Studies on the Relationship Between Photosynthesis and Nitrogen Fixation in the Symbiotic System of Soybean and Nodule Bacteria( Rhizobium)

The relationship between photosynthesis of soybean and nitrogen fixation of the nodules by symbiotic Rhizobium was studied. The contents of total nitrogen and chlorophyll, the net photosynthetic rate and seed yield of soybean were much higher in either hydroponically cultivated or field-grown plants inoculated with Rhizobium B16–11C (or Clark nodulating strain) than in control without inoculation (or Clark non-nodulating strain). These results show that the symbiotic nitrogen fixation has a beneficial effect on photosynthesis. However, the effect was indirect and slow so that there was no change in the net photosynthetic rate of the soybean leaves until three clays after removing nodules from the soybean roots. On the other hand, decreasing the photosynthate supply to nodule by shade, defoliation or shoot removal of the soybean, the nodule activity declined significantly. It seems that the supply of photosynthate to root nodule is a limiting factor for symbiotic nitrogen fixation. However, the diurnal variation of the nodule activity could not be explained by change neither in the contents of sucrose and starch of the root nodules nor in the ambient temperature. The factor controlling the diurnal variation deserves further study.     

丛枝菌根真菌和根瘤菌对白三叶氮同化的影响

为揭示丛枝菌根真菌(AMF)和根瘤菌在白三叶氮(N)同化中的作用,该研究对白三叶进行单一或联合接种隐类球囊霉(Paraglomus occultum)和三叶草根瘤菌(Rhizobium trifolii),分析其对白三叶的生长、光合作用、叶片N和氨基酸含量以及N同化相关酶活性的影响。结果表明:(1)单一接种AMF或根瘤菌以及联合接种AMF和根瘤菌均显著增加了白三叶的株高、匍匐茎长度、叶片数、地上部生物量、总生物量、叶绿素b和总叶绿素含量、稳态光量子效率和叶片N含量,这种增强效应是联合接种>单一AMF>单一根瘤菌>未接种处理。(2)联合接种AMF和根瘤菌显著增加了白三叶叶片中丙氨酸、精氨酸、天冬酰胺、天冬氨酸、谷氨酰胺、谷氨酸和组氨酸的含量,显著提升了叶片N同化相关酶如硝酸还原酶、亚硝酸还原酶、谷氨酰胺合成酶、谷氨酸合成酶、谷氨酸脱氢酶、天冬酰胺合成酶和天冬氨酸转氨酶的活性,显著促进AMF对白三叶根系的侵染。综上认为,联合接种AMF和根瘤菌通过激活N同化相关酶活性有效促进N同化,产生更多氨基酸,进一步促进白三叶植株生长; 联合接种AMF和根瘤菌具有协同作用,有效促进了白三叶的N同化。     

典型草原建群种羊草对氮磷添加的生理生态响应

由于人类活动和气候变化的共同作用, 大气氮(N)沉降日益加剧, 使得陆地生态系统中的可利用性N显著增加, 生态系统更易受其他元素如磷(P)的限制。然而, 目前关于N、P养分添加对草原生态系统不同组织水平的影响研究较少, 相关机制尚不清楚。该文以内蒙古典型羊草(Leymus chinensis)草原为研究对象, 通过连续两年(2011-2012年)的N和P养分添加实验, 研究建群种羊草的生理生态性状、种群生物量和群落初级生产力对N、P添加的响应及其适应机制。结果表明: 羊草草原不同组织水平对N、P添加的响应不同。群落水平上, 地上净初级生产力在不同降水年份均受N和P元素的共同限制, N、P共同添加显著提高了地上净初级生产力; 物种水平上, N、P添加对羊草种群生物量和密度, 以及相对生物量均没有显著影响, 表明羊草能够维持种群的相对稳定; 个体水平上, 在正常降水年份(2011年), 羊草生长主要受N素限制, 而在湿润年份(2012年), 降水增加使得羊草生长没有受到明显的养分限制。羊草通过增加比叶面积、叶片大小和叶片N含量, 提高整体光合能力, 以促进个体生长。总之, 内蒙古典型草原群落净初级生产力受N、P元素共同限制, 作为建群种的羊草, 其对N、P添加的响应因组织水平而异, 也受年际间降水变化的影响。     

Arbuscular mycorrhiza infection enhances the growth response of Lolium perenne to elevated atmospheric pCO(2)

Elevated atmospheric pCO(2) increases the C-availability for plants and thus leads to a comparable increase in plant biomass production and nutrient demand. Arbuscular mycorrhizal fungi (AMF) are considered to play an important role in the nutrient uptake of plants as well as to be a significant C-sink. Therefore, an increased colonization of plant roots by AMF is expected under elevated atmospheric pCO(2). To test these hypotheses, Lolium perenne L. plants were grown from seeds in a growth chamber in pots containing a silica sand/soil mixture for 9 weeks with and without inoculation with Glomus intraradices (Schenck and Smith). The growth response of plants at two different levels of N fertilization (1.5 or 4.5 mM) combined with ambient (35 Pa) and elevated atmospheric pCO(2) (60 Pa) was compared. The inoculation with G. intraradices, the elevated atmospheric pCO(2) and the high N fertilization treatment all led to an increased plant biomass production of 16%, 20% and 49%, respectively. AMF colonization and high N fertilization increased the plant growth response to elevated atmospheric pCO(2); the plant growth response to high N fertilization was also increased by AMF colonization. The root/shoot ratio was reduced by high N fertilization or elevated atmospheric pCO(2), but was not affected by AMF colonization. The unchanged specific leaf area indicated that if AMF colonization represented an increased C-sink, this was fully covered by the plant. Elevated atmospheric pCO(2) strongly increased AMF colonization (60%) while the high N fertilization had a slightly negative effect. AMF colonization neither improved the N nor P nutrition status, but led to an improved total P uptake. The results underline the importance of AMF for the response of grassland ecosystems to elevated atmospheric pCO(2).     

Nitrogen supply affects arbuscular mycorrhizal colonization of Artemisia vulgaris in a phosphate-polluted field site

Root colonization by arbuscular mycorrhizal fungi (AMF) was investigated in industrially polluted grassland characterized by exceptionally high phosphorus levels (up to 120 g kg(-1) soil). Along a pollution-induced nitrogen gradient, soil and tissue element concentrations of Artemisia vulgaris plants and their mycorrhizal status were determined. Additionally, we compared mycorrhization rates and above-ground biomass of A. vulgaris at N-fertilized and control plots in the N-poor area. Despite high soil and tissue P concentrations, plants from N-deficient plots, which were characterized by low tissue N concentrations and N : P ratios, were strongly colonized by AMF, whereas at a plot with comparable P levels, but higher soil and plant N concentrations and N : P ratios, mycorrhization rates were significantly lower. Correlation analyses revealed a negative relationship between percentage root colonization of A. vulgaris by AMF and both tissue N concentration and N : P ratio. Accordingly, in the fertilization experiment, control plants had higher mycorrhization rates than N-fertilized plants, whereas the species attained higher biomass at N-fertilized plots. The results suggest that N deficiency stimulates root colonization by AMF in this extraordinarily P-rich field site.     

Compatibility of Rhizobial Genotypes within Natural Populations of Rhizobium leguminosarum Biovar viciae for Nodulation of Host Legumes

Populations of Rhizobium leguminosarum biovar viciae were sampled from two bulk soils, rhizosphere, and nodules of host legumes, fava bean (Vicia faba) and pea (Pisum sativum) grown in the same soils. Additional populations nodulating peas, fava beans, and vetches (Vicia sativa) grown in other soils and fava bean-nodulating strains from various geographic sites were also analyzed. The rhizobia were characterized by repetitive extragenomic palindromic-PCR fingerprinting and/or PCR-restriction fragment length polymorphism (RFLP) of 16S-23S ribosomal DNA intergenic spacers as markers of the genomic background and PCR-RFLP of a nodulation gene region, nodD, as a marker of the symbiotic component of the genome. Pairwise comparisons showed differences among the genetic structures of the bulk soil, rhizosphere, and nodule populations and in the degree of host specificity within the Vicieae cross-inoculation group. With fava bean, the symbiotic genotype appeared to be the preponderant determinant of the success in nodule occupancy of rhizobial genotypes independently of the associated genomic background, the plant genotype, and the soil sampled. The interaction between one particular rhizobial symbiotic genotype and fava bean seems to be highly specific for nodulation and linked to the efficiency of nitrogen fixation. By contrast with bulk soil and fava bean-nodulating populations, the analysis of pea-nodulating populations showed preferential associations between genomic backgrounds and symbiotic genotypes. Both components of the rhizobial genome may influence competitiveness for nodulation of pea, and rhizosphere colonization may be a decisive step in competition for nodule occupancy.     

Arbuscular mycorrhizal fungi influence water relations, gas exchange, abscisic acid and growth of micropropagated chile ancho pepper (Capsicum annuum) plantlets during acclimatization and post-acclimatization

Little is known about the role of arbuscular mycorrhiza fungi (AMF) on physiological changes of micropropagated plantlets during acclimatization and post-acclimatization. Using chile ancho pepper (Capsicum annuum L. cv. San Luis), measurements were made of water relations, gas exchange, abscisic acid (ABA), plantlet growth and AMF development. Plantlets had low photosynthetic rates (A) and poor initial growth during acclimatization. Relative water content (RWC) decreased during the first days after transfer from tissue culture containers to ex vitro conditions. Consequently, transpiration rates (E) and stomatal conductance (gs) declined, confirming that in vitro formed stomata were functional and able to respond ex vitro to partial desiccation--thus avoiding excessive leaf dehydration and plant death. Colonization by AMF occurred within 3 days after inoculation. Colonized plantlets had lower leaf ABA and higher RWC than noncolonized (NonAMF) plantlets during peak plant dehydration (6 days after plant transfer)--and a higher A and gs as early as days 5 and 7. During post-acclimatization [after day 8, when RWC increased and stabilized], A increased in all plantlets; however, more dramatic changes occurred with AMF plantlets. Within 48 days, 45% of the roots sampled of inoculated plantlets were colonized and had extensive arbuscule development. At this time, AMF plantlets also had greater E, A, leaf chlorophyll, leaf elemental N, P and K, leaf dry biomass and leaf area, fruit production and differences in carbon partitioning [lower root/shoot ratio and higher leaf area ratio] compared with NonAMF plantlets. Rapid AMF colonization enhanced physiological adjustments, which helped plantlets recover rapidly during acclimatization and obtain greater growth during post-acclimatization.     

Compatibility of rhizobial genotypes within natural populations of Rhizobium leguminosarum biovar viciae for nodulation of host legumes

Populations of Rhizobium leguminosarum biovar viciae were sampled from two bulk soils, rhizosphere, and nodules of host legumes, fava bean (Vicia faba) and pea (Pisum sativum) grown in the same soils. Additional populations nodulating peas, fava beans, and vetches (Vicia sativa) grown in other soils and fava bean-nodulating strains from various geographic sites were also analyzed. The rhizobia were characterized by repetitive extragenomic palindromic-PCR fingerprinting and/or PCR-restriction fragment length polymorphism (RFLP) of 16S-23S ribosomal DNA intergenic spacers as markers of the genomic background and PCR-RFLP of a nodulation gene region, nodD, as a marker of the symbiotic component of the genome. Pairwise comparisons showed differences among the genetic structures of the bulk soil, rhizosphere, and nodule populations and in the degree of host specificity within the Vicieae cross-inoculation group. With fava bean, the symbiotic genotype appeared to be the preponderant determinant of the success in nodule occupancy of rhizobial genotypes independently of the associated genomic background, the plant genotype, and the soil sampled. The interaction between one particular rhizobial symbiotic genotype and fava bean seems to be highly specific for nodulation and linked to the efficiency of nitrogen fixation. By contrast with bulk soil and fava bean-nodulating populations, the analysis of pea-nodulating populations showed preferential associations between genomic backgrounds and symbiotic genotypes. Both components of the rhizobial genome may influence competitiveness for nodulation of pea, and rhizosphere colonization may be a decisive step in competition for nodule occupancy.     

干旱胁迫条件下AMF促进小马鞍羊蹄甲幼苗生长的机理研究

采用温室水分控制试验,在干旱胁迫条件下,定量化研究优势丛枝菌根真菌(AMF)影响优势乡土植物小马鞍羊蹄甲(Bauhinia faberi var.microphylla)幼苗生长的机理,主要通过研究干旱胁迫条件下摩西球囊霉菌(Funneliformis mosseae)与小马鞍羊蹄甲的共生关系,阐明AMF在植物生长初期的作用。结果表明,干旱胁迫条件下,摩西球囊霉菌能够很好地侵染幼苗,侵染率高达89%—97%,并且不受水分条件影响。接种的幼苗最大光合速率、水分利用效率随着干旱胁迫程度从重度到轻度(水分从低到高)逐渐增大,相反地,叶片脯氨酸含量逐渐减小。接种显著地促进幼苗株高、叶片数、叶面积、根长、根面积等生长指标,提高幼苗各部分生物量、地上地下磷(P)含量。当含水量为60%田间持水量时,AMF促进小马鞍羊蹄甲幼苗吸收P的效果最好。接种还显著影响幼苗的生物量分配,在重度干旱胁迫时影响P分配,水分条件也显著影响幼苗的生物量分配。此外,接种和水分的交互作用对叶生物量、总生物量、生长指标以及地上部氮(N)总量影响显著。结果表明干旱胁迫条件下菌根效应显著,并在干旱条件下显著促进了小马鞍羊蹄甲幼苗的生长,这为进一步干旱河谷植被恢复提供了理论依据。     

Synergistic effect of colonization with arbuscular mycorrhizal fungi improves growth and drought tolerance of Plukenetia volubilis seedlings

The objective of this study was to investigate the effects of arbuscular mycorrhizal fungus (AMF) inoculation on plant growth and drought tolerance in seedlings of a promising oilseed crop, Sacha Inchi (Plukenetia volubilis L.), under well-watered or drought conditions. AMF inoculation was applied in four treatments: without AMF inoculation, Glomus versiforme, Paraglomus occultum, or combination of both microorganism inoculations. The results showed that AMF colonization significantly enhanced the growth of Sacha Inchi seedlings regardless of soil water conditions, and the greatest development was reached in plants dually inoculated under well-watered conditions. G. versiforme was more efficient than P. occultum. Plants inoculated with both symbionts had significantly greater specific leaf area, leaf area ratio and root volume when compared with the uninoculated control, G. versiforme, and P. occultum treatments alone, indicating a synergistic effect in the two AMF inoculation. Photosynthetic rate and water-use efficiency were stimulated by AMF, but not stomatal conductance. Inoculation with AM fungus increased antioxidant enzymes activities including guaiacol peroxidase and catalase, thus lowering hydrogen peroxide accumulation and oxidative damage, especially under drought stress conditions. However, proline content showed little change during drought stress and AMF colonization conditions, which suggested that proline accumulation might not serve as the main compound for osmotic adjustment of the studied species. These results indicate that AMF inoculation stimulated growth and enhanced drought tolerance of Sacha Inchi seedlings, through alterations in morphological, physiological and biochemical traits. This microbial symbiosis might be an effective cultivation practice in improving the performance and development for Sacha Inchi plants.     

黑果枸杞功能性状对氮磷添加的响应及其可塑性

分析养分添加对荒漠植物功能性状的影响,对揭示其响应和适应环境变化的规律至关重要。本研究以黑果枸杞为材料,设置3个氮磷(NP)添加量(低、中、高)和N/P(5∶1、15∶1、45∶1),量化分析了整株、根、茎、叶和果实性状对NP添加的响应。结果表明: 黑果枸杞功能性状差异化响应了NP添加量和比例,随NP添加量的增加,生物量和比叶面积增加,根冠比、叶干物质含量、根组织密度和比根长降低;随N/P的提高,地下生物量、比根长和净光合速率增大。17个功能性状指标的变异系数为7.3%～69.1%,生物量、根冠比和比根长为响应氮磷的敏感性状(可塑性指数PI>0.5),变异性较大(49.4%～69.1%);而叶长宽比、叶厚、叶组织密度、叶茎干物质含量为惰性性状(PI<0.20)。主成分分析(PCA)结果显示,黑果枸杞在多元特征空间的位置随NP添加量横向迁移,趋向于地上、地下生物量更大、根冠比更小的策略;同时叶组织密度与叶厚、比叶面积呈负相关;叶干物质含量与叶厚、比叶面积呈负相关,与叶组织密度呈正相关;生物量与比叶面积呈正相关,与比根长呈负相关。逐步回归分析进一步表明,比根长、比叶面积和叶片净光合速率是影响黑果枸杞生物量的主要功能性状。黑果枸杞通过资源利用策略的转变、根系碳分配的改变以及性状的权衡协变与非一致性响应适应土壤养分环境的波动。     

丛枝菌根真菌与根瘤菌互作及类黄酮对互作效果的影响

研究了中华根瘤菌与AM真菌互作或加入适量的类黄酮(150nmol·L^-1和1．5μmol·L^-1)对紫云英的生物量、结瘤数、AM真菌的侵染率、菌丝ALP和SDH酶活性的影响．结果表明,与对照组[0、AMF、Rh]相比,Rh+AMF组紫云英的生物量、结瘤数、AM真菌侵染率和菌丝酶活都有显著差异;与对照组及Rh+AMF组相比,类黄酮处理组紫云英的生物量、结瘤数、AM真菌侵染率和菌丝酶活差异更加显著,但不同类黄酮间(apigenin和hesperitin),或同一种类黄酮不同浓度处理问(150nmol·L^-1和1．5umol·L^-1)差异不明显,说明AM真菌与根瘤菌互作对紫云英的结瘤固氮、AM真菌的侵染和菌丝的生长都有促进作用．当Rh+AMF组加入适量的类黄酮时。这种促进作用更加显著．     

Defoliation effects on mycorrhizal colonization, nitrogen fixation and photosynthesis in the Glycine-Glomus-Rhizobium symbiosis

Soybean [ Glycine max (L.) Merr. cv. Wells] plants grown in a greenhouse were inoculated with Rhizobium japonicum strain 61A118 and the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum (Thaxt. sensu Gerd.) Gerd. & Trappe. Plants were defoliated (26, 48 and 66%) throughout the growth period and evaluated for VAM colonization, N₂, fixation and photosynthesis at harvest (six weeks). Photosynthate stress as a result of defoliation affected nodulation and nodule activity most severely. Colonization of the roots by the VAM fungus was little affected in comparison, and the intensity of colonization increased with increasing stress. The CO₂-exchange rate decreased less with defoliation than did leaf mass, and photosynthetic efficiency increased with the severity of defoliation. The increase in photosynthetic efficiency was significantly correlated with increases in leaf P (r = 0.91) and N (r = 0.97) concentrations. The results suggest that the VAM fungus should not be regarded as a simple P source and C sink in the tripartite legume association. Threeway source/sink relationships (VAM-P, Rhizobium-N, and host leaf-C) are discussed.     

Influence of phosphorus and nitrogen on photosynthetic parameters and growth in <Emphasis Type="Italic">Vicia faba</Emphasis> L.

The influence of phosphorus (P) and nitrogen (N) supply on biomass, leaf area, photon saturated photosynthetic rate (P_max), quantum yield efficiency (α), intercellular CO₂ concentration (C_i), and carboxylation efficiency (CE) was investigated in Vicia faba. The influence of P on N accumulation, biomass, and leaf area production was also investigated. An increase in P supply was consistently associated with an increase in N accumulation and N productivity in terms of biomass and leaf area production. Furthermore, P increased the photosynthetic N use efficiency (NUE) in terms of P_max and α. An increase in P supply was also associated with an increase in CE and a decrease in C_i. Under variable daily meteorological conditions specific leaf nitrogen content (N_L), specific leaf phosphorus content (P_L), specific leaf area (δ_L), root mass fraction (R_f), P_max, and α remained constant for a given N and P supply. A monotonic decline in the steady-state value of R_f occurred with increasing N supply. δ_L increased with increasing N supply or with increasing N_L. We tested also the hypothesis that P supply positively affects both N demand and photosynthetic NUE by influencing the upper limit of the asymptotic values for P_max and CE, and the lower limit for C_i in response to increasing N.     

干旱胁迫下AMF对云南蓝果树幼苗生长和光合特征的影响

采用盆栽试验与称重控水法,将土壤相对含水量分别控制在田间最大持水量的100%、91.68%、82.85%、60.00%、41.86%和21.28%,并在这6个不同的土壤相对含水量条件下,分别设添加苯菌灵(杀真菌剂)(低AMF)和不添加苯菌灵(高AMF)处理,研究干旱胁迫下AMF对极小种群野生植物云南蓝果树幼苗生长和光合特征的影响,揭示云南蓝果树濒危的微生物学机制,为云南蓝果树保护措施的制定与实施奠定基础。结果表明,添加苯菌灵处理显著降低了不同水分条件下的AMF侵染率,说明试验中AMF处理的实生苗在生长和光合特征上的差异是苯菌灵处理下侵染率下降导致的;随着干旱胁迫的加剧,云南蓝果树幼苗的根部AMF侵染率显著降低、叶面积等生长指标和净光合速率(Pn)等光合参数都发生显著变化;高AMF处理可以显著增加水分充足和轻度干旱胁迫条件下云南蓝果树幼苗的大部分生长指标和光合参数,而对重度胁迫下的云南蓝果树幼苗没有显著影响,说明重度干旱胁迫对其影响大于AMF的影响;另外,整合了可塑性指数分析和隶属函数分析两种方法对其抗旱性进行评价,云南蓝果树幼苗基本上无法通过调节形态和光合能力来适应水分环境的变化,但是高AMF处理可使云南蓝果树幼苗具有较强的可塑性和更强的抗旱性。实验结果为云南蓝果树的科学保育及种苗繁育提供了理论依据。     

Arbuscular mycorrhizal fungi and organic fertilizer influence photosynthesis,root phosphatase activity,nutrition, and growth of <Emphasis Type="Italic">Ipomoea carnea</Emphasis> ssp. <Emphasis Type="Italic">fistulosa</Emphasis>

The effect of arbuscular mycorrhizal fungi (AMF) inoculation and organic slow release fertilizer (OSRF) on photosynthesis, root phosphatase activity, nutrient acquisition, and growth of Ipomoea carnea N. von Jacquin ssp. fistulosa (K. Von Martinus ex J. Choisy) D. Austin (bush morning glory) was determined in a greenhouse study. The AMF treatments consisted of a commercial isolate of Glomus intraradices and a non-colonized (NonAMF) control. The OSRF was applied at 10, 30, and 100 % of the manufacturer’s recommended rate. AMF plants had a higher net photosynthetic rate (P _N), higher leaf elemental N, P, and K, and generally greater growth than NonAMF plants. Total colonization levels of AMF plants ranged from 27 % (100 % OSRF) to 79 % (30 % OSRF). Root acid phosphatase (ACP) and alkaline phosphatase (ALP) activities were generally higher in AMF than non-AMF plants. When compared to NonAMF at 100 % OSRF, AMF plants at 30 % OSRF had higher or comparable ACP and ALP activity, higher leaf elemental P, N, Fe, Cu, and Zn, and a greater P _N (at the end of the experiment), leading to generally greater growth parameters with the lower fertility in AMF plants. We suggest that AMF increased nutrient acquisition from an organic fertilizer source by enhancing ACP and ALP activity thus facilitating P acquisition, increasing photosynthesis, and improving plant growth.